Ruthenium Terpyridine Complexes Containing a Pyrrole-Tagged 2,2鈥?Dipyridylamine Ligand鈥擲ynthesis, Crystal Structure, and Electrochemistry
文摘
Ruthenium(II) terpyridine complexes containing the pyrrole-tagged 2,2鈥?dipyridylamine ligand PPP (where PPP stands for N-(3-bis(2-pyridyl)aminopropyl)pyrrole with the general formula [Ru(tpy)(PPP)X]n+ (1, X = Cl鈥?/sup>; 2, X = H2O; 3, X = CH3CN; tpy = 2,2鈥?6鈥?2鈥?terpyridine) have been synthesized and characterized by 1H NMR, IR, UV鈥搗is, mass spectrometry, and elemental analysis. 1 and 2 have been structurally characterized by X-ray crystallography. Both 1 and 2 were successfully immobilized onto glassy carbon electrode via anodic oxidation of the pyrrole moiety on the PPP ligand to give stable and highly electroactive polymer films. Cyclic voltammetric studies of 1 in acetonitrile revealed a RuIII/RuII couple at 0.4 V vs Cp2Fe+/0 initially, but another redox couple resulting from chloride substitution by acetonitrile developed at E1/2 = 0.82 V upon repetitive potential scan. This ligand substitution was induced by the acidic local environment caused by the release of protons during pyrrole polymerization. The electropolymerization of 2 in aqueous medium allowed the observation of the formation of RuIV鈺怬 species in polypyrrole film. As the film grew thicker, the size of the RuIII//RuII couple (E1/2 = 0.8 V vs SCE at pH 1) of poly[Ru(tpy)(PPP)(OH2)]n+ increased accordingly, whereas the growth of the RuIV/RuIII couple (E1/2 = 0.89 V vs SCE at pH 1) leveled off after the film had reached a certain thickness. The Pourbaix diagram of the E1/2 of the RuIII /RuII and RuIV/RuIII couples vs pH of the electrolyte medium has been obtained. The resulting poly[Ru(tpy)(PPP)(OH2)]n+ film is electrocatalytically active toward the oxidation of benzyl alcohol.